Adsorption kinetics between thiolated polyethylene glycol (SH-PEG) and mercaptoproprionic acid (MPA) on gold nanoparticles (Au-NP) were studied using dynamic light scattering (DLS) and electrospray differential mobility analysis (ES-DMA). Through a cumulant analysis, the changes in hydrodynamic z-average particle size due to the formation of SH-PEG coatings on Au-NPs were measured by DLS in both two component (Au-NP + MPA or SH-PEG) and three component (Au-NP +MPA + SH-PEG) systems. ES-DMA was employed to quantify the surface coverage of SH-PEG and establish a correlation function between surface coverage and the change in particle size measured by DLS. A change in equilibrium binding constant for SH-PEG on Au-NPs at various concentrations of SH-PEG and MPA showed that the presence of MPA reduced the binding affinity of SH-PEG to the Au-NP surface. Kinetic studies showed SH-PEG was desorbed from the Au-NP surface following a second-order desorption model after subsequently introducing MPA. The desorption rate constant of SH-PEG from the Au-NP surface by MPA displacement was strongly affected by the concentration of MPA and the excess SH-PEG in solution.